The present invention is based on a fuel injector of the type set forth in the main claim.
A fuel injector is referred to in U.S. Pat. No. 4,766,405, having a valve-closure member, connected to a valve needle, which acts together with a valve seat surface formed on a valve seat element to form a sealing seat. A magnetic coil is provided for electromagnetically actuating the fuel injector, the magnetic coil acting together with an armature which is connected to the valve needle by force-locking. Around the armature and the valve needle an additional cylindrical mass is provided, which is connected to the armature via an elastomeric layer.
It is believed that a disadvantage with this fuel injector may include a costly construction method with an additional component. In addition, the large surface elastomer ring is unfavorable for the pattern of the magnetic field and may hinder the closing of the field lines, and thus the achievement of great attractive forces during the opening movement of the fuel injector.
A specific embodiment of a fuel injector is also referred to in the above document in which, for damping and debouncing, a further cylindrical mass is provided around the armature and the valve needle, which is hemmed in and held in its position by two elastomeric rings. When the valve needle strikes the valve seat, this second mass may move relatively to the armature and the valve needle and prevent bouncing of the valve needle.
It is believed that a disadvantage of this specific embodiment may include an additional cost and requirement for space. Also, the armature is not decoupled, whereby its impulse on the valve needle may increase the tendency to bouncing.
A fuel injector having a valve needle and an armature is referred to in U.S. Pat. No. 5,299,776, in which the armature is movably guided on the valve needle, and the movement of which in the lift direction of the valve needle is limited by a first stop and, opposite to the lift direction, by a second stop. The play in the movement of the armature in the axial direction, fixed by the two stops, leads within certain limits to a decoupling of the inert mass of the valve needle as well as the inert mass of the armature. Within certain limits, this counteracts the bouncing back of the valve needle from the valve seat surface when the fuel injector is closed. However, since the axial position of the armature with respect to the valve needle is totally undefined, due to the free movement of the armature, bounces may be avoided to only a limited extent. In particular, with regard to the method of construction of the fuel injector referred to in the above document, what is not avoided is that the armature strikes the stop facing the valve-closure member during a closing movement of the fuel injector and transfers its linear momentum to the valve needle. This impact-like transfer of linear momentum may cause additional bounces of the valve-closure member.
Furthermore, the armature guided on the valve needle may be fastened by an elastomeric ring in a position in which it is movably clamped. To do this, the armature may be held between two flanges welded to the valve needle, there being an elastomeric ring between the armature and the lower flange. With this arrangement, however, a borehole through the armature may be necessary for the supply of fuel to the sealing seat. The boring through the armature is made close to the valve needle, the opening of the boring facing the valve seat being partially covered by the elastomeric ring. Thereby a nonuniform compression of the elastomeric ring arises, and the bore edges finally lead to the destruction of the elastomeric ring by the pressure of the edges. Additionally, this may cause excitation of vibrations of the unsupported elastomeric ring, which may also contribute to the trouble. caused by the bore edges. This may occur, for example, at low temperatures, when the elastomer converts into a stiff condition.
By contrast, an exemplary fuel injector according to the present invention may have the advantage that the armature and the valve needle are damped by a fluid damper that is formed between the armature and the valve needle by the collaboration of an elastomeric ring and a fluid-filled chamber. This may stop armature bounces from the lower armature as well as effectively damp valve needle bounces from the sealing seat.
It is believed that the damping action of the damping space between valve needle and armature wall into which fuel is squeezed from the annular space during the closing movement is an advantage.